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5G Wireless Technology: Paving the Road to the Internet of Things (IoT)

Courtesy of Rogers Corporation Blog

in Advanced Connectivity Solutions, by sharilee

You think the pace of technology innovation is fast now, wait til you see what’s going to happen with 5G wireless. 5G will drive an Internet of Things (IoT) ecosystem of intelligent, fully connected sensors and devices, capable of improving economies small and large, and further blurring geographical borders.

According to the 2017 Cisco Mobile Visual Networking Index (VNI), 5G networks will be able to support advanced applications such as remote surgery, immersive experiences through virtual and augmented reality, autonomous cars, and so on.” All are game changers in their industries.

By 2021, it is predicted there may be as many as 25 billion 5G-capable devices and connections globally. The first few years of IoT deployment will run mostly on LTE networks using NarrowBand IoT (NB-IoT) and LTE M. But 5G growth is expected to be fast.

The Cisco VNI report states, “While 4G was the network that made smartphones prolific as a personal infotainment device, 5G is going to be network of the IoT. 5G will be capable of offering a new high bandwidth benchmark of 1 Gbps or higher and sub 1 ms latency. Operationally, 5G’s support for dynamic resource allocation and application prioritization will accommodate a variety of M2M devices, including those that require very low bandwidth.”

Today’s cellular networks operate in the 700 MHz to 2.6 GHz bands. Mobile service providers have introduced 4.5G and 4.9G technology to improve speeds immediately. 5G fixed wireless access will follow shortly; Verizon has been running trials in 11 cities. 5G mobile technology will follow shortly; AT&T estimates as soon as late 2018.

5G, when it arrives, is expected to handle far more traffic at much higher speeds than current cell network base stations. This requires new technologies, including millimeter waves (mmWaves), massive MIMO (multiple-input multiple-output), beamforming, and full duplex. Let’s take a look at a few of these key developments.

Millimeter Wave Spectrum

5G networks will be based on millimeter wave technology that can run in the underutilized portions of the 10-300 GHz band. Some cellular providers have begun to use mmWaves to send data between stationary points, such as base stations. Providers are considering the next step, using millimeter waves to connect mobile users to nearby base stations.

They are called mmWaves because the wavelength varies in length from 1 to 10 mm vs. the radio waves that serve today’s wireless devices, which measure tens of centimeters in length. Because these signals are shorter, there are hurdles to overcome. The higher frequencies carry more data, but are easily blocked by buildings and foliage, and sometimes even rain.

Sub-6 GHz Spectrum

Certain frequencies under Sub-6 GHz will be defined as 5G frequencies by 3GPP. That means these defined frequencies will be included in 5G standards and will apply to all countries.

A wide range of 5G trials are underway across the globe. China Mobile recently demonstrated the first 5G remote driving technology using a consumer car. They also completed a commercial Massive MIMO deployment that attained speeds of 2 Gbps.

In Massive MIMO, a high number of antennas, potentially hundreds, are incorporated into advanced chips that are smaller, deliver more processing power, and use less battery. The large number of antennas helps minimize signal loss and energy consumption, and can mitigate obstruction issues by steering signals in specific directions.

The Challenge of High Frequency Materials

Designers of these high frequency devices need to balance cost, weight, size, and radiation characteristics (such as gain, beamwidth, side-lobe levels, polarization). High frequency circuit materials deliver the performance needed by wireless base stations, satellite antennas, and network servers and storage.

PCB materials with dielectric constant (Dk) values of about 2.8 to 3.5 are preferred for sub-6 GHz and millimeter wave circuit applications. The consistency of the Dk across a circuit board can also be an important concern at these frequencies since variations in the Dk can introduce variations in the signal phase. Performance can also be affected by the composition of the PCB material.

Given this challenging set of requirements, what types of real-world materials are suitable for sub-6 GHz and millimeter-wave circuits?

The majority of initial 5G applications will be under 6 GHz, frequencies that are similar to those used in 3G and 4G materials. For such applications:

  • Rogers’ RO4350B laminates provide tight control of Dk and low loss. They are rigid thermoset materials that do not use PTFE, but can achieve excellent RF/microwave performance over time and even at elevated temperatures.
  • The RO4835 laminates are a high-performance material for high-frequency applications, but because it is not based on PTFE, it does not require special preparation (such as a sodium etch) to enable the formation of reliable plated through holes.

For microwave and millimeter wave applications:

  • The RO4730G3™ UL 94 V-0 antenna-grade laminates are designed to meet present and future performance requirements in active antenna arrays and small cells, in 4G base transceiver stations (BTS) and Internet of Things (IoT) applications, as well as emerging 5G wireless systems. These flame-retardant (per UL 94V-0), thermoset laminate materials are an extension of Rogers’ dependable RO4700™ circuit materials, which are a popular choice for base station antennas. RO4730G3 laminates provide the low dielectric constant (Dk) of 3.0 favored by antenna designers, held to a tolerance of ±0.05 when measured at 10 GHz.

Other new technologies are being created to enable the IoT networks that will deliver valuable insight obtained from massive amounts of data:

  • High temperature silicone materials serve as gaskets and seals, cushions, and thermal and acoustic insulation in demanding and remote environments.
  • Laminated multilayer busbars provide efficient and compact connections for propulsion, auxiliary, and other IGBT based converters in connected car and connected rail systems.

5G and sub-6 GHz networks will impact every aspect of our lives. Finding the right balance of material performance and cost is a challenge, especially technologies that is are still being defined.

RO3203 Laminate by Rogers Corporation

Courtesy of www.everythingrf.com

The RO3203 from Rogers Corporation are ceramic-filled laminates reinforced with woven fiberglass. The dielectric constant of RO3203 high frequency circuit materials is 3.02 with a dissipation factor of  0.0016 up to frequencies as high as 40 GHz. RO3200 series laminates are manufactured under an ISO 9002 certified quality system. These laminates are ideal for automotive collision avoidance systems, direct broadcast satellites, power backplane and base station infrastructure applications.

Product Specifications

  • Manufacturer : Rogers Corporation
  • Description : High Frequency Ceramic-Filled Laminates with Woven Fiberglass
  • Dk (Dielectric Constant) : 3.02
  • Df (Dissipation Factor) : 0.0016
  • Td : 500 Degrees C
  • Surface Resistivity : 107 MOhms
  • Volume Resistivity : 107 MOhms.cm
  • Dimensional Stability : 0.8 mm/m
  • Tensile Modulus : 351 and 409 kpsi
  • Thermal Coeffecient : -13 ppm/Degree C
  • Thermal Conductivity : 0.48 W/m/K

www.rogerscorp.com

PCB Laminates: Discovering Dielectric Constant (Dk)

This post authored by John Coonrod, Technical Marketing Manager, and team originally appeared on the ROG Blog hosted by Microwave Journal.

Dielectric constant (Dk) is one of the most important of circuit material parameters and a starting point for circuit designers. The dimensions of high-frequency circuit structures, including different types of transmission lines and the spacing between lines for proper isolation and/or coupling, are determined by the circuit material’s dielectric characteristics. One of the main parameters for understanding those characteristics is Dk. Circuit designers typically grow familiar with different commercial circuit materials, whether flexible or rigid, and may even gain great understanding of how to work with a material having a certain Dk value, such as 3.0.  Many designers grow to trust that the Dk value assigned to a given circuit material is truly accurate and consistent from board to board and base their designs on that trust. But how does the material supplier determine a circuit material’s Dk value anyway?

A circuit laminate’s Dk can be determined by different measurement techniques, generally using a microwave vector network analyzer (VNA) to evaluate the amplitude and phase characteristics of reference circuits with fairly well-known behavior. Such reference circuits include microstrip and stripline transmission lines as well as various types of resonators. By fabricating two microstrip transmission lines of different lengths on a circuit laminate with precisely known thickness, for example, and measuring the phases of the two lines with a VNA, the difference in phase values between the two transmission lines can provide insight into the Dk of the circuit material.

It sounds straightforward, but there is much to consider in this seemingly simple measurement. For one thing, most circuit laminates are anisotropic in nature, with different Dk properties along different axes of a material. A circuit material that has been characterized with a Dk value of 3.0 through the z axis of the material at a certain frequency may not exhibit the same Dk values through its x and y axes (length and width). The use of microstrip transmission lines to determine circuit material Dk via differential-phase-length method is an effective means of discovering a Dk value through the z axis of the material. But it is a measurement that must be performed with precision, with the electrical effects of a test fixture’s connectors removed from the phase values measured for the transmission lines. And this is just one of many test methods used in the RF/microwave industry to determine laminate Dk; some additional test methods provide Dk through the z axis while others help determine Dk through the x and y axes of the material. Some of these test methods are also used to measure a material’s dissipation factor (Df).

It is also important to remember that a circuit laminate’s Dk value depends on frequency, with 10 GHz often used as the test frequency for determining the Dk of a particular circuit material. If a circuit material is characterized for a given Dk value at 10 GHz using a test approach such as the microstrip differential-phase-length method, it will exhibit a different Dk value if tested with the same measurement method at a different frequency. And, unfortunately, two different Dk test methods may not even yield the same values of Dk for the same material under test even at the same test frequency!

A number of circuit material Dk test methods are based on fabricating resonators or resonant cavities on a material and evaluating the performance of the resonator. This use of perturbed resonators yields Dk values that are typically through the x and y axes of the material and can also help determine the material’s Df. One such method, for example, is the use of a split post dielectric resonator (SPDR) to measure both Dk and Df as outlined in application note 5989-5384E from Agilent Technologies (now Keysight Technologies), “Agilent Split Post Dielectric Resonators for Dielectric Measurements of Substrates.” The SPDR method, one of the approaches used by Rogers Corp. (along with the differential-phase-length method) to evaluate Dk, is a means of measuring Dk automatically with a VNA and test software at a single frequency. It provides in-plane Dk value through the length and width of a substrate but is not effective beyond a certain thickness and Dk value of material.

The different test methods employed by different circuit material suppliers may lead to some confusion for engineers comparing different circuit materials in search of a laminate with a certain Dk value for a design. It is important to note the test frequency at which the Dk has been characterized as well as which axis or axes for which the Dk value has been determined. Of course, for engineers working on the growing number of millimeter-wave circuit applications, such as for short-haul communications or automotive electronic safety systems (radar), Dk values referenced to a test frequency of 10 GHz offer little insight into how a circuit material will behave at frequencies above 30 GHz and it is at these higher frequencies that work remains to be done in characterizing circuit material Dk.

Fortunately, suppliers of commercial circuit laminates are aware of the differences among the various Dk and Df measurement approaches and are working together to try to eliminate confusion for engineers comparing laminate data sheets, especially in terms of Dk. The IPC D-24C Task Group of the noted global trade association, Association Connecting Electronics Industries, and its Institute of Printed Circuits (IPC) is attempting to better understand the impact of different test methods on determining the Dk values of high-frequency circuit laminates and is focused on broadband VNA measurements above 10 GHz for determining Dk and Df values for circuit laminates.

The task group, which includes leading materials test companies and suppliers of RF/microwave circuit laminates, is developing precise methods for testing the same circuit materials from the same production lots, not only with different test methods but at different locations along a board, to better understand all of the variables involved in determining precise, repeatable Dk and Df values for a circuit material. One of the goals of the task group is to establish reliable test methods for Dk and Df above 10 GHz as well as repeatable measurement techniques for determining precise values of material thickness, another important material parameter for circuit designers. Hopefully, this industry teamwork and the efforts of the task group members will yield circuit laminate data sheets that can be compared easily and with confidence.

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For Millimeter-Wave Performance, Thinner Materials are Often Better

Thin can be a good thing for high-frequency circuit laminate materials. As this ROG Blog detailed some years ago (see “Thinner Materials Help Target Higher Frequencies,” http://mwexpert.typepad.com/rog_blog/2010/11/thinner-materials-help-target-higher-frequencies.html), thinner printed-circuit-board (PCB) laminates offer many electrical benefits as well as mechanical advantages compared to thicker circuit materials, especially at higher frequencies reaching into millimeter-wave bands. For applications where weight and size are critical, such as circuits for portable and mobile products, thinner circuit laminates are important starting points that can lead to miniature, lightweight solutions. In terms of electrical performance, thinner laminates offer many benefits over thicker circuit materials, in particular for microstrip circuits operating at millimeter-wave frequencies.

Microstrip is one of the most widely used transmission-line technologies for RF/microwave circuits. As the ROG Blog has noted many times, microstrip circuits are highly dependent upon the choice of circuit laminate for optimum performance. The best microwave performance results from the right mix of circuit material parameters, such as consistent dielectric constant (Dk) and high-quality copper conductor layers, right down to the thickness of the laminate. Ideally, microstrip circuits fabricated on the right laminate composition and thickness will achieve excellent electrical performance with low loss and minimal unwanted resonances or spurious signals.

However, thicker circuit laminates can pose problems for microstrip circuits, with the thickness measured as substrate only and without the thickness of the copper included. When microstrip circuits are fabricated on thicker laminates, unwanted resonances can occur. These resonances arise between a laminate’s metal layers and can disrupt the desired signal propagation of the quasi-transverse-electromagnetic (quasi-TEM) waves through the microstrip transmission lines.

Excessive conductor width can also be a concern when attempting to minimize spurious generation in microstrip circuits. If microstrip signal conductors are wider than one-eighth wavelength at the design frequency, resonances can occur between the edges of the conductors. These spurious-mode resonances can interfere with the desired signal propagation through the microstrip conductors. Since wavelengths shrink with increasing frequencies, attention must be paid to circuit structures and circuit material dimensions to avoid such opportunities for spurious generation. At millimeter-wave frequencies (above about 30 GHz), in particular, where the wavelengths become extremely diminutive, careful balance is critical between circuit laminate thickness and circuit dimensions for optimum circuit performance.

Those smaller wavelengths call for thinner laminates to minimize any opportunities for spurious signal generation. At the same time, narrow circuit conductors can help prevent any generation of edge-to-edge conductor resonances. At higher frequencies, microstrip conductors are typically designed and fabricated for a controlled impedance, such as 50 Ω, to achieve signal transference with low losses and minimal reflections. The consistently narrow conductor widths required to achieve a controlled impedance across a PCB also provide the circuit physical conditions needed to minimize edge-to-edge conductor resonances.

As noted in the earlier ROG Blog, the Dk of the circuit laminate also plays a role in determining the circuit dimensions required for a particular design impedance, including the conductor widths. For a given laminate thickness, design frequency, and microstrip impedance, the circuit dimensions will shrink with increasing value of Dk. As a result, circuit miniaturization can be achieved by designing and fabricating microstrip and other transmission-line technologies on circuit laminates with higher Dk values.

Thinner circuits offer benefits in terms of controlling electromagnetic interference (EMI). As microstrip circuits increase in frequency, they also tend to radiate more EM energy. When the level of radiated EM energy becomes excessive, it can interfere with the proper operation of the circuit from which it originates as well as any circuits nearby. When compared at the same high operating frequency, thinner microstrip circuits will radiate less EM energy than thicker circuits, so that thinner circuits have the potential for less EMI problems. Less radiation loss also equates to less signal loss for a microwave circuit.

Microstrip is a practical and straightforward transmission-line approach for many high-frequency circuit designs, but it may not always be the best choice for all designs, especially those sensitive to the effects of spurious signals and radiation. Grounded coplanar waveguide (GCPW) is an alternative transmission-line technique that has proven effective for minimizing spurious modes and EM radiation. It can be used with thicker circuit laminates, although better results can be achieved with thinner circuit materials. When comparing microstrip and GCPW for the same circuit material and material thickness, GCPW circuitry has much less spurious generation and suffers much less EM radiation than microstrip circuitry for the same operating frequency.

The choice of transmission-line technology and circuit laminate thickness at higher frequencies can also be influenced by whether or not dispersion is a concern.  Dispersion is a characteristic of transmission lines and circuit substrate materials in which different transmission lines may exhibit different group velocity or group delay with frequency, essentially with the smaller waves of higher frequencies slowing down as a result of the transmission lines. For narrowband circuits, dispersion is not a problem. But it can be problematic for broadband circuits, for longer circuits (with longer delays), and for pulsed waveforms, since the time for a high-speed pulse to travel through one type of transmission line will not be the same as for a transmission line with longer group delay. Transmission lines differ in their dispersion characteristics: microstrip and some types of waveguide suffer longer group delays compared to nondispersive transmission-line formats like stripline and GCPW.

For higher-frequency circuits, GCPW can minimize dispersion compared to microstrip, but it can also be more challenging to manufacture at higher frequencies, especially with the fine dimensions and circuit features required for millimeter-wave frequency operation. GCPW is more sensitive to the copper plating thickness variation due to the PCB fabrication process than microstrip, and can suffer circuit-to-circuit performance variations in insertion loss and phase response as a result of variations in laminate copper plating thickness. The inherent advantages of GCPW over microstrip in terms of dispersion characteristics can be nullified unless a circuit with tight tolerance in copper plating thickness is specified, along with tightly controlled Dk and overall laminate thickness. Thinner circuit materials can provide many benefits, provided that the tolerances of those circuit laminates are tightly controlled.

www.rogerscorp.com

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